Radar on the Great LakesFebruary
1947 Radio News Article

Wax nostalgic about and learn from the history of early electronics.
See articles from Radio &
Television News, published 1919 - 1959. All copyrights hereby acknowledged.

An article title with both 'radar' and 'Great Lakes' (I live a mile
from Lake Erie) in the title is sure to catch my attention, as did
this. Author Norman Schorr reports on the state of the art of radar
equipment and usage for the purpose of maritime navigation. Research
and development, along with an ample surplus of components left
over from World War II facilitated a rapid adaptation of radar
to many venues. Included among its applications were airway and
waterway navigation, rocket trajectory tracking, security systems,
speed measurement, weather observation, and aerial mapping. It is
easy to take for granted the capabilities of radar today with having
the accumulated knowledge of more than half a century on our side,
but pioneers in the field had to think everything up anew. I have
to admit to being familiar with what a 'Pliotron'
was prior to reading this article (it is Irving Langmuir's high
frequency version of the Audion vacuum tube).

Radar on the Great Lakes

By Norman A. Schorr

Characteristics of six different types of radar installations
now operating as test units aboard lake carriers.

The ship "George F. Rand" was assigned to
Raytheon for their radar installation. The wave guide run from
the antenna to transmitter is 70 feet. The indicator, housing
a 7" PPI, can be tilted 45 degrees vertically and rotated through
45 degrees horizontally.

A dense fog suddenly descended on Lake Erie the morning of April
27, 1944. War shipping was at its height on this narrowest and most
heavily-trafficked of the five Great Lakes. Within a few hours,
two collisions occurred that cost the lives of 12 crew members and
the loss of two cargo-laden ships. Without warning, the ore-carrier
James H. Reed, collided head-on with the steamer Ashcroft, and sank
quickly off Conneaut, O. Seventy-five miles west, the 4000-ton Frank
E. Vigor, carrying a load of sulphur from Chicago to Buffalo, foundered
and sank after colliding with the Philip Minch.

Accidents like these are rare in Great Lakes shipping history.
In fact, they have occurred on Lake Erie an average of once in 20
years since the advent of steel vessels in 1886. Stringent traffic
rules, a special system of whistle signals, carefully routed up
and down courses, and more recently radio telephone, radio beams
and direction finders have combined to hold down the number of accidents.

But still they have occurred - and when they do, the need for
all-weather navigation instruments is emphasized.

Though collisions caused by fogs have been infrequent, it is
not unusual for skippers to be forced to drop the hook and wait
until adverse weather conditions lift. Fog is encountered frequently
in the spring and fall, and occasionally at other times. In the
late fall, storms of sleet and snow can be expected. In a recent
year more than 4,000,000 gross tons of cargo space were lost as
a result of delays, collisions and groundings due to fog. Bad weather
has held up ships for as long as 30 hours. As many as 100 boats
have been fog-bound at the locks of the Sault Sainte Marie canal
at one time.

Great Lakes shippers took an immediate interest in radar as soon
as the first successful marine application became known. Experience
of the Coast Guard with radar during the war was watched as closely
as security regulations permitted. A few sets were installed for
brief trial runs, but extensive equipment for thorough experimentation
was not available. It was not until after V-J Day that the shippers
through their Lake Carriers Association initiated an active program,
called the Radar Operational Research Project, to develop radar
equipment best suited for Lake operations.

They needed a navigation aid that would make possible close-range
sailing in thick weather. Such a radar design would of necessity
have high accuracy and definition at close quarters and would be
capable of clearly showing shore lines, other ships, and the comparatively
small buoys and channel markers.

It was decided that the radar research men and engineers should
be brought in direct contact with Great Lakes navigation personnel,
so that each group might become familiar with the problems of the
other. To this end, radar manufacturers were invited to install
sets aboard a Lake cargo vessel during the 1946 season. Six manufacturers
accepted the invitation and each was assigned a different ship on
which to make an experimental installation that would operate on
the Lakes. Upon conclusion of test runs and evaluation of results,
minimum operating specifications will be set forth.

Since the Lake Carriers Association represents 90 per-cent of
the bulk cargo carried on the Lakes, this project is being followed
with great interest in marine shipping circles, particularly with
regard to inland waterway navigation.

The busy Great Lakes are connected chiefly by rivers and dredged
channels, some of which are no more than 600 or 700 feet in width.
On an average trip a freighter will spend 25 to 30 per-cent of the
time traveling in these confined waters.

Among the most tortuous of these are in the entrance to the locks
of the Sault Sainte Marie Canal between Lakes Superior and Huron;
the Strait of Mackinac between Huron and Michigan; the St. Clair
flats and Detroit River between Huron and Erie and the Welland Canal
between Erie and Ontario.

The parabolic reflector in the scanner component
of the Sperry Gyroscope marine radar is 48 inches by 18 inches
and rotates 360 degrees in azimuth at about 15 revolutions per
minute. Contained in the splash-proof box are a driving motor
(split-phase 1/8 horsepower squirrel cage induction motor) and
a type SG synchro generator.

One of the narrowest and most inadequate of the dredged channels
is the 700-foot wide Southeast Bend around Harsens Island, in the
delta of the St. Clair River. It is in an area subject to sudden
fog. Up and down traffic must squeeze through a 2-1/2 mile stretch
of reverse bends that afford slight clearance. Each section the
Bend sees about 20,000 vessel passages, carrying 90 to 100 million
tons of ore, coal, grain and stone.

Another tight spot is the 4-1/2 mile long West Neebish Channel,
down bound from the Sault Canal. There, shores are as low or lower
than a vessel's deck. Three miles of the channel are only 600 feet
wide. Then it narrows for 5000 feet to a width of only 300 feet,
and a depth of 24 feet, 8 inches - blasted through rock.

Typical ones of the larger bulk cargo vessels are 600 feet or
more long, 60 feet wide and travel at a speed of 11 to 13 land miles
per hour. All in all there are about 800 commercial vessels of both
American and Canadian registry plying the Lakes, almost half of
them major type vessels.

During busy times there is a two-way procession of ships going
through the man-made locks and channels sometimes only 15 minutes
apart. It is not difficult to visualize how impairment of visibility
as a result of fog, sleet or other thick weather can seriously hamper
traffic and even paralyze all navigation.

During fogs, a phenomenon known as "aberration of sound" often
occurs and contributes to make navigation more hazardous. On such
occasions, "dead spots" appear on the Lakes. In these areas whistle
signals from approaching vessels either cannot be heard or are distorted
so that they seem to come from a source other than their true one.

Other aspects of Great Lakes shipping that affect the job that
radar is being called on to perform:

Extreme length of travel in the Lakes from Duluth to Montreal
is more than 1300 miles, but the main movement of ships is over
the 1000-mile run between the upper Lakes and Lake Erie. Sailing
season averages eight months, from about April to December, when
the Lakes are free of ice. During this period a bulk cargo vessel
may travel a distance equal to 2 1/2 times the earth's circumference
at the equator, making port at least twice a week, for about 4 to
5 hours at a time.

Compared to similar salt water vessels, these Lake carriers are
somewhat larger and travel a few miles faster. During the war they
delivered 4 1/2 times the total tonnage carried by all of America's
merchant marine fleet on salt water.

The master of one of these vessels cannot sail down the winding
course of a river or channel by setting a compass course as is done
in ocean sailing. He must follow a course marked by buoys of various
sorts. At night his course is indicated by red and green lights
on top of these markers, in addition to a heading taken on the range
lights. When the skipper reaches an open lake area the widely separated
up and down courses are followed by compass bearings in reference
to special shore lights.

Unlike the salt water master he cannot call on a harbor pilot, and
a tug or two, to guide him into each of the 80-odd major ports on
the United States and Canadian shores. He himself controls all the
ship's movements from the time she raises anchor in the spring until
she is laid up at the end of the season. An additional navigation
problem is presented by the fact that many of the Lakes harbors
are located at mouths of rivers.

This was the picture when the radar manufacturers entered the
program last year.

The surface search sets they installed are principally simplified
versions of the military and naval designs in widespread use during
the war. They are designed for reliable operation without the attention
of technical personnel. A navigator can operate a radar set after
an hour of practice. Installed to give a maximum over-all view of
the horizon, they furnish a continuous radar picture of the waters
surrounding a ship, detecting the presence and location of shorelines,
buoys, lighthouses and other vessels, with respect to the radar-equipped
ship.

Modulator section of the Westinghouse set
is located in the weatherproof base of the antenna pedestal.
Action of the sine-wave oscillator, blocking oscillator, and
thyratron tube, all shown in the picture. triggers the magnetron
2000 times per sec.

Unlike military radar sets which included the so-called A-type
indicator, the simplified marine radar sets depend solely on the
PPI (Plan Position Indicator) to give the ship's navigator range
and bearing information. This is accomplished by transmitting short
pulses of ultra-high frequency radio energy at a rapid rate. These
powerful radio waves are concentrated in a beam that is narrow in
the horizontal plane and comparatively wide in the vertical plane.
They strike objects in their path and are scattered. A small fraction
of the original waves is reflected back to the rotating antenna,
which in the interval between pulses serves as the receiving antenna.
The reflected waves are amplified and fed to the fluorescent screen
of a cathode ray tube where they are translated into spots of light.

Factors governing the determination of a range reading include
an object's size, shape, reflectivity, height, radar sensitivity
and the wavelength of the radar set. But in general, radar horizon
is the basic limiting factor for maximum range readings. In other
words, a large object will loom higher on the horizon and will offer
a larger reflecting surface; hence it will be able to be detected
at greater distances.

Since radio waves travel at a constant speed of 186,000 miles
per second - like light - measurement of the time it takes for a
signal to travel out and bounce back gives a reliable reading of
range, or the distance between the ship and the object. On the sets
in this project, readings are accurate to within approximately one
or two per-cent.

The face of the scope is calibrated in miles. Maximum range can
be varied, in steps, depending on how large an area the operator
wishes to scan. Concentric marker rings, equally spaced, can be
superimposed on the screen of the cathode ray tube to aid in estimating
range. The minimum range at which an object can be detected is 100
yards and the maximum with any of the sets is 50 miles.

Radio frequency head of the Westinghouse
set is also installed in the lower section of the antenna pedestal.
It contains the magnetron oscillator, the crystal detector,
local oscillator, and the high-frequency circuits associated
with them.

Transmitting a pulsed high-frequency signal is accomplished in
this way: A high voltage pulse of microsecond duration causes a
magnetron to oscillate. The resultant signal is sent to the antenna
through a wave guide or coaxial system and directed into space by
a reflector.

Reflected energy is returned to the transmitter and detected
in an r.f. section, where an i.f. signal is produced according to
the superheterodyne principle. The i.f. signal is then amplified
and detected. This time a video signal is the result and it is sent
to the PPI indicator circuits, modulating a narrow electron beam.
This beam shows up as a line of light on the scope face, and as
it rotates, leaves a trail of objects visible to the observer as
bright spots.

In order that range information be accurate, indicator circuits
are timed to start the electron beam's radial sweep each time the
magnetron emits a pulse. As a burst of energy leaves the antenna
the beam in the tube starts its movement toward the rim, and completes
its journey in the interval between pulses. It is in this interval
that the reflected signal is picked up by the antenna and fed to
the PPI.

Rotation of the antenna is linked to the magnetic deflection
coils around the CRT, thus synchronizing the rotation of the electron
beam. Since the high frequency energy travels in straight lines
and at such great speeds, the reflections show up in proper bearing.

As the antenna's beam sweeps across the bow of a ship, a radio
line called a "heading flasher" is intensified on the PPI. When
the picture is stabilized with North at the top of the scope, this
flasher indicates ship's direction or heading.

Equipment for azimuth stabilization is provided with some sets
to furnish a bearing with respect to true North. This is possible
when a ship is equipped with a gyro-compass.

The radar picture is a continually changing one, and therefore
the direction of any moving object may be noted. The path of another
ship can be "observed" through a fog; and together with the use
of navigational charts and standard techniques of seamanship, safe
travel is made possible under adverse conditions.

Indicator console in the Westinghouse installation.
Below the seven-inch PPI and its controls and circuits are the
low voltage power supply and the intermediate and video frequency
amplifiers.

A GE parabolic reflector installed atop the
pilot house of the "Ernest T. Weir." First Mate Gallaqher and
Captain Hartman are inspecting the installation.

In addition, an indication of an object's physical composition
also be learned from the blobs of light on the scope face. Shore
lines are clearly outlined; rain appears as feathery masses. Buoys
show up as small, but distinct dots. Ships may be accurately outlined,
but more frequently resemble oval-shaped objects. A towing a barge
often can be distinguished from two separate ships.

To help the receiver provide an accurate scope picture under
varying conditions, it is equipped with STC (sensitivity time control),
FTC (fast time constant) and AFC (automatic frequency control circuits).

STC suppresses "sea return," which is the reflection of signals
from waves or particles of water. These signals impair observation
of close target objects in rough weather. The STC circuit increases
the receiver gain automatically with range, and is usually available
to the operator in steps.

FTC breaks up large signals caused by interference or by closely-grouped
targets. It is particularly usefu. in detecting objects like channel
buoy in heavy "sea return" or heavy rain.

Automatic frequency control stabilizes receiver tuning with respect
to the magnetron frequency.

Since one antenna is used for transmission and reception, the
sensitive receiver must be protected during transmission periods.
This is accomplished by a transmit-receive tube which fires and
effectively short-circuits the receiver every time an outgoing pulse
travels toward the antenna. To prevent any reflected power from
being wasted by going to the quiescent magnetron between pulses,
an anti-transmit-receive tube that presents a large impedance to
the signal is employed.

The sets are designed to operate an alternating current power
supply of 115 volts and 60 cycles, principally. For vessels where
primary power is d.c., a suitable motor-generator set is used. A
detachable viewing hood is provided to aid in observing the scope
under unfavorable light conditions.

One fundamental difference among the various sets is found in
the operating frequencies. Four (Radiomarine, Sperry), Westinghouse,
and Western Electric) are built to operate on the "X" band or three
cm. wavelength. The Raytheon and GE models operate on the "S" band,
with a 10 cm. wavelength.

Supporters of the "X" band contend it provides better definition,
better azimuth discrimination and hence is better for piloting a
ship in close quarters. They also claim it furnishes greater range
for a given radar sensitivity. "S" band advocates claim more reliability
in bad, rainy weather, and less interference from "sea return."

Determination of which band is superior for operation on the
Great Lakes, is one of the hoped-for results of the project, although
at the time of this writing it has not been decided whether all
regularly-installed radar sets on Great Lakes ships will be limited
to one band or the other.

Other differences and similarities can be discovered in an examination
of some of the different sets (see Table 1).

One of the 10 cm. sets, Raytheon's "Mariners Pathfinder," was
installed on the self-unloader bulk freighter George F. Rand in
August. Operating frequency is 3070 megacycles ± 50 mc. Range
scales are 1.5, 5, 15, and 50 miles. All exposed parts of the set
are designed to withstand temperature from ,-40°C to ,60°C.
The indicator, housing a seven-inch CRT and mounted on a pedestal,
is movable. It can be tilted 45 degrees in a vertical plane and
rotated 45 degrees in a horizontal plane.

The transmitter, receiver, modulator and associated components
are built in one unit. In the transmitter, pulse rate is 1000 cycles
and pulse length is 0.4 microseconds. Peak power output is more
than 15 kw. Source of radio frequency, of course, is the magnetron.
In the receiver, a 30 megacycle i.f. is used; the r.f. band pass
is 3 mc.

The truncated parabolic antenna, 7 feet wide and 18 inches high,
is installed on top of the ship's "A" frame, necessitating a waveguide
run of approximately 70 feet. Antenna rotation is 7 r.p.m., both
clockwise and counter-clockwise. It gives a beam approximately 3.5
degrees at half power points in horizontal plane. In the vertical
plane the beam width is about 15 degrees. While proceeding on Lake
Erie, gas buoys were observed at ranges of four to five miles. Ships
were observed from 20 to 25 miles. A rainstorm, about 10 by 30 miles
in area, was picked up and plotted. When the Rand entered the storm
area, vessels and other targets were accurately observed. In the
Detroit River channel, buoys, piers, and even rowboats were detected
at limited ranges.

The other 10 cm. set is the General Electric "Electronic Navigator"
installed on the 8000 ton steamer E. T. Weir. It uses a 7-inch PPI,
with fixed range scales of 2, 6 and 30 miles. A true or relative
bearing can be obtained by direct reading from a movable bearing
cursor with respect to a movable Azimuth scale.

The 4 1/2 foot high viewing console contains all the radio equipment.
Peak power output is the 7 kw, minimum output from the magnetron.
Pulse length is 0.5 microseconds maximum, and pulse repetition rate
is 1500 cycles per second. This frequency is determined by a blocking
oscillator which simultaneously keys the modulator (pliotron tube)
and the gate for the sweep generator.

Captain Hartman, a veteran of more than 40
years' service on the Great Lakes studies the PPI of the General
Electric "electronic: navigator" aboard ship.

Modulator and r.f. head of Westinghouse radar
set, including microwave section, a.f.c. control, and preamplifier.

The reflector, a cast aluminum truncated parabola, makes about
11 r.p.m. and gives a beam width of five degrees to the half power
points in the horizontal and 17 degrees to the half power points
in the vertical.

Cathode-ray tube deflection system of Radiomarine's radar set.

The Radiomarine 3 cm. installation made in September on the A.
H. Ferbert, operates on a frequency of 9320-9430 megacycles. It
consists of three major units: oscilloscope indicator, antenna assembly
and transmitter-receiver. A four-foot high indicator cabinet houses
a 12-inch cathode ray tube, associated circuits and power supply.

Rotating the CRT's electron beam in synchronism with the rotation
of the antenna, for accurate bearing data, is achieved electronically
without use of a moving coil. Single phase saw-tooth energy from
synchronizer circuits is fed through coaxial cable to a size 5 G
Synchro generator located in the antenna assembly, and three-phase
modulated saw-tooth waves are produced. This energy then is sent
through a 5 DG (differential generator) to a stationary deflection
coil around the neck of the CRT, and this coil controls beam rotation.
A 5 DG is not required on a ship without gyro compass. Since the
differential generator is driven from the gyro compass, a stabilized
picture always is obtained, so that "UP" position on the scope always
points to North. A true or relative bearing can be obtained by merely
flipping a switch, without recalibration.

A gyro repeater scale is mounted at the head of the PPI, to indicate
ship's course at all times, whether radar is on or off. Range can
be varied from 1 1/2, to 5, 15 and 50 miles.

The transmitter and receiver are built into a rectangular cabinet
about five feet high, installed in the wheelhouse. Capable of delivering
a peak power output of approximately 30 kw., the transmitter has
two sets of pulse rates. For short distance operation, the pulse
length is 0.25 microseconds and pulse rate is 3000 cycles. For longer
ranges, the pulse length becomes 1 microsecond and the pulse rate
750 cycles.

An 18-inch high parabolic cylinder antenna is constructed of
curved, spaced stainless steel rods and rotates at 10 r.p.m. It
uses a horn-type feed. Mounted on a standard 16 1/2 inch Navy flange,
the lower section of the antenna assembly includes a driving motor,
synchro generator, gearing and the wave guide rotary joint.

The Westinghouse "X" band set was installed in July aboard the
William G. Mather while the ship was underway. It gives readings
for areas with radii of 2, 8 and 32 miles. On the wheelhouse roof
a cut paraboloidal antenna is mounted, in a round plastic dome on
a 5 1/2 foot pedestal. This pedestal also houses the driving a.c.
motor, related drive gears and a" so-called synchro-tie system to
coordinate the circular movement of antenna with rotation of electron
beam.

Antenna unit of the Radiomarine radar installed
on top of the pilot house of the "A. H. Ferbert." The 18 inch
high parabolic cylinder is constructed of spaced stainless steel
rods and rotates at 10 r.p.m. Lower part of antenna assembly
includes a driving motor, synchro generator, gearing and the
wave guide rotary joint.

In the weather proof base of the pedestal are the modulator,
high voltage power supply, preamplifier and the r.f. head, which
includes magnetron oscillator, the synthetic type crystal detector
and local oscillator. The r.f. components are mounted in the antenna
pedestal to cut possible power attenuation between transmitter and
antenna,

The 7-inch PPI scope is mounted on a four-foot high cabinet,
on the ship's bridge, called the indicator console. Within this
cabinet are the low voltage power supply, the i.f. and video amplifiers
and related PPI circuits.

The magnetron is triggered 2000 times a second by the action
of a sine wave oscillator, blocking oscillator and thyratron tube,
and emits a 0.4 microsecond pulse. Peak power out­put is more than
15 kw. Conducted by a horn-type wave guide to the radiator, the
signal is sent out in a vertical fan pattern, two degrees wide horizontally
and about 15° vertically. The radiator rotates at 12 r.p.m.

In the receiver, a constant i.f. signal of 60 megacycles is provided
by action of a klystron local oscillator.

The Sperry 3 cm. set was installed on the Frank Armstrong in
August, on a trip from Cleveland. It consists of an antenna assembly,
viewing binnacle and transceiver unit which contains transmitter
and receiver. Three internally-adjustable ranges can be set up on
the 12-inch PPI; the first, from 100 yards to 2-5 miles, second,
500 yards to 6-12 miles, third, 1 mile to 20-40 miles.

Fixed electronic range markers, appearing at regular intervals,
are provided for each scale; in addition there is a variable marker.
Range at this marker can be read to the nearest 100 yards directly
from a counter. To permit clearer definition of close targets, the
ship's own position indicator at the center of the scope can be
expanded.

This set can also be used in conjunction with the Coast Guard
radar beacons, or racons, originally designed for aircraft navigation.
By turning a control switch, the operator can bring in only signals
from a beacon. These appear now as a series of short lines, coded
to indicate the particular beacon. Provision is made so that the
set will be able to operate with the new beacons designed for marine
use.

Pulse width is 0.25 microsecond and 1000 cycles a second for
radar; 2 microseconds and 400 cycles per second for beacon operation.
Peak power output is 35 kw. The parabolic cylinder reflector, four
feet wide and 18 inches high emits a beam 2 degrees or less in the
horizontal plane, and more than 15 degrees in the vertical plane.
It rotates at 15 r.p.m.

Last of the 3 cm. sets is the Western Electric radar which actually
was the first of the six to be installed. Just before it went into
operation aboard the John T. Hutchinson a "Miss Radar of the Great
Lakes" christened the antenna with a bottle containing water from
all of the Lakes.

The installation consists of three basic units: the antenna on
the pilot house, the indicator cabinet inside the pilot house, and
the transmitter-receiver and synchronizer cabinets in the chart
room.

Pulse length of the transmitted signal is of 0.5 microsecond
duration and a frequency of 1000 cycles per second. The truncated
parabolic antenna, made of laminated aluminum, turns at 12 r.p.m.
It emits a beam pattern 15 degrees in the vertical plane and two
degrees in the horizontal. The range scale is variable and can be
adjusted to cover an area with a radius from one to 40 miles.

Because of delays in installation of some of the sets the operational
phase of the research project will extend into the early part of
the 1947 shipping season, according to C. M. Jansky, the electronics
engineer who heads the project committee. For this reason recommended
standards for future sets will not be issued until later this year.

General reports have indicated that the sets have worked well.
Ship personnel have caught on to radar quickly and are enthusiastic
about its effectiveness. In one period when traffic approaching
the St. Mary's River below the Sault locks was stalemated because
of fog, two of the six radar-equipped ships were able to proceed
straight to the locks and continue on their way. A performance like
that is the best salesman radar can have.

To simplify the task of observing the PPI picture in coincidence
with navigation charts, two methods have been developed and are
under consideration for future addition to the equipment. One will
be to project a microfilm of a radar-piloting chart on the PPI screen;
the other is to superimpose the scope picture directly on a navigation
chart by means of a reflectoscope or similar device.

In addition to its value for close range navigation, radar's
ability to gather long-range information is expected to be helpful
in expediting ship movements under the rapidly-changing weather
conditions found on the Lakes.

Ship operators predict a brilliant career for radar in one of
its first and biggest peacetime assignments.

In the words of Captain C. O. Rydholm, marine superintendent
of the Cleveland-Cliffs Iron Company, which is a member of the Lake
Carriers Association: "We believe radar will enable us to move cargoes
with maximum speed, and, although our captains have set an enviable
record of safe operations over the years, we believe radar will
afford us an extra measure of safety for crews, cargo, and ships."